1. Field of the Invention
The present invention relates to a method of preparing L-aspartyl-D-.alpha.-aminoalkanecarboxylic acid-(S)-N-.alpha.-alkylbenzylamide which is a sweetener.
2. Discussion of the Background
Present eating habits have involved an increase intake of sugars compared to past diets, resulting in an increase in obesity and other diseases. To avoid these problems many low-calorie sweeteners have been developed as alternatives to sugar. For example, aspartame, is widely used and has excellent safety and sweetness quality. Unfortunately, aspartame is relatively unstable; therefore, it is desirable to find a sweetener with improved stability.
U.S. Pat. No. 5,286,509 discloses L-aspartyl-D-.alpha.-aminoalkanecarboxylic acid-(S)-N-.alpha.-alkylbenzyla mide which has a higher sweetness and a higher stability than aspartame and is a promising compound as a dietary sweetener. N-benzyloxy-carbonyl-L-aspartic acid .beta.-benzylester in which the amino group and the .beta.-carboxylic group of L-aspartic acid are protected is condensed with D-.alpha.-aminoalkanecarboxylic acid-(S)-N-.alpha.-alkylbenzylamide using dicyclohexylcarbodiimide, and then the benzyloxycarbonyl and benzyl groups are removed by catalytic hydrogenation to yield the product. However, this method is not suitable for industrial production since it employs two expensive materials, N-benzyloxy-carbonyl-L-aspartic acid .beta.-benzylester as a raw material and dicyclo-hexylcarbodiimide as a condensation agent.
U.S. Pat. No. 5,286,509 also describes that N-protected-L-aspartic anhydride such as N-benzyloxy carbonyl-L-aspartic anhydride or N-formyl-L-aspartic anhydride can be alternatively employed, but no specific processes or conditions are disclosed.